1. Field of the Invention
The present invention relates to a method of preventing transmission spurious response in a radio transceiver, and in particular, to a method of preventing transmission spurious response in a receiver section and a radio transceiver.
2. Description of the Related Art
In a conventional transceiver using a time division duplexing (TDD) system, a transmission frequency is quite similar to or equal to a reception frequency.
Consequently, it is pretty difficult to attenuate sufficiently a component of the transmission signal which leaks into the reception signal by using only a band-pass filter.
Japanese Patent Laid-Open application No. 9-116459 describes a technology to remove such interference in a radio transceiver having an antenna used commonly for transmitting and receiving signals. According to the laid-open application, an apparatus to remove interference between transmission and reception signals operates as follows. In a transceiver in which, as shown in FIG. 1, a transmission signal fed from a transmitting section 31 via band-pass filter (BPF) 32 which limits bandwidth of transmitting signal is applied via first metallic path 41 to transmission and reception circulator 33 and guided into antenna 34 by circulator 33, and reception signal fed from antenna 34 is delivered by circulator 33 to band-pass filter 35 which passes the reception signal via second metallic path 43 and transferred to receiver section 36 after filtering.
The transceiver further comprises circulator 45 which distributes transmission signal between transmitting section 31 and circulator 33, receiver side directional coupler 44 between receiving section 36 and circulator 33 and third metallic path 42 including amplifier 51 and phase shifter 52 between circulator 45 and coupler 44. The difference between a length of the path from circulator 45 via first and second paths 41 and 42 to coupler 44 and an associated length therefrom via third path 42 to coupler 44 is set to xcex/2 (xcex=wavelength) or an odd-number multiple thereof so as to cancel a leakage component of the transmission signal.
The leakage component of the transmission signal flows into an input port of receiving section 36 due to, for example, a reverse directional or directive distribution of circulator 33. Using coupler 44, a leak signal from circulator 45 is regulated in amplitude and phase by amplifier 51 and phase shifter 52 to be fed via third path 42 as a transmission signal component.
The signal component cancels interference caused by the leakage transmission signal via metallic path 43 through circulator 33. This cancellation secures removal of interference between the transmission and reception signals even when these signals are similar in frequency to each other. Therefore, the radio frequency bandwidth can be efficiently used by minimizing the difference between the frequencies.
The technology of the laid-open application is effective in that the leakage transmission wave from circulator 45 is canceled through the matching operation with the path length, the amplitude, and the phase shift to resultantly suppress interference between transmission and reception. However, the laid-open application describes no measure to remove a transmission spurious response component having a frequency similar to the transmission frequency.
In the transceiver using the TDD system, when the transmission signal is transmitted, a high powered transmission signal is inputted into the receiving amplifier even if it is not supplied power yet, causing to generate a distortion due to non-linear characteristic of input stage of the receiving amplifier and generates not only expected receiving signal frequency but unexpected harmful frequencies so called as the spurious response.
Particularly, in a transceiver using two transmission frequencies at the same time, components of the two transmitting signals having different frequencies enter into a receiver thereof via unexpected routes. This causes intermodulation distortion and hence transmission spurious response.
An object of the present invention to provide a transmission spurious response preventing method in which a leakage signal due to a transmission signal sent from a transmitter with a high power is prevented by canceling the leakage signal with a signal having opposed phase and the same amplitude to the leakage transmission signal.
Another object of the invention is to provide a transceiver which operates in a time division duplex (TDD) system and has a receiving amplifier including an input port connected to an antenna system selected for a signal transmission.
The transceiver is also provided means for supplying a signal divided from the transmission signal and having the same amplitude and opposite phase to the amplitude and phase of the leakage transmission signal into the input port of the receiving amplifier which is connected to an antenna selected for the transmission, for canceling the leakage transmission signal.
The radio transceiver further includes a first circulator for separating a transmission and reception path, a transmitting amplifier, and a second circulator disposed in an outlet side of the transmitting amplifier. The transmission signal is supplied via the first circulator to the antenna, and the division of the transmission signal for use of canceling is fed via the second circulator to the receiving amplifier.
In accordance with the present invention, a radio transceiver operating in a time division duplex (TDD) transmission including: an antenna used commonly for transmitting and receiving signals; a first circulator of rotary insulating type connected to the antenna; a receiving section for receiving a signal via a first strip line and a receiving amplifier from said first circulator; a transmitting amplifier for high-frequency amplifying a transmission signal; a second circulator connected to an output port of said transmitting amplifier; a third strip line and a fourth strip line for establishing connection between a normal directivity outlet from said second circulator to said first circulator; and a sixth strip line and a seventh strip line for establishing connection between a reverse directivity outlet from said second circulator and an input port of said receiving amplifier of the receiving section.
In the transceiver, a transmission signal reached to the input port of the receiving amplifier via a first path including normal directivity outlet of the second circulator, said third strip line, said fourth strip line, reversed directivity outlet of said first circulator, said first strip line, and the input port of said receiving section, and a transmission signal reached to the input port of the receiving amplifier via a second path including the reverse directivity outlet of said second circulator, said sixth strip line, said seventh strip line, are equal in amplitude and reverse in phase to each other.
There is provided in accordance with the present invention a transmission spurious response preventing method used for a radio transceiver operating in a time division duplex (TDD) transmission, wherein the method includes the step of inputting a high-frequency signal delivered from a transmitting amplifier to an input port of a receiving amplifier of a receiving section connected to an antenna system selected for a signal transmission to cancel a leakage transmission signal by setting the amplitude of the delivered transmission signal the same to the leakage transmission signal and setting the phase of the delivered transmission signal to reversed relativity with the leakage transmission signal.
Conceptually, the transmission spurious response preventing method of the present invention is implemented in a radio transceiver operating in a TDD including a unit which supplies an input port of a receiving amplifier connected to an antenna system selected for transmission with a transmission signal having a phase inverted with respect to a phase of a leak transmission signal from the antenna so as to suppress the spurious emission component taking place in the receiving amplifier.
More specifically, as can be seen from FIG. 2, a signal from transmitting amplifier 11 is fed via a second circulator 13 and a third strip line 14 to a first switch 15. The signal is then delivered via a fourth strip line 16 and a first circulator 2 to a first antenna 1 to be sent therefrom. Or, the signal is fed via a fifth strip line 17 and a third circulator 7 to a second antenna 2 to be transmitted therefrom. In this situation, most power of the transmission signal inputted to first or third circulator 2 or 7 is supplied to the associated antenna. However, the power is partly delivered via a first strip line 3 to a first receiving amplifier 4 or via a second strip line 8 to a second receiving amplifier 9. Also in second circulator 13, the transmission signal inputted thereto is partly fed via a sixth strip line 18 to a second switch 19. Second switch 19, a third switch 21, and a fourth switch 23 operate under control of a signal from a controller 24 to couple sixth strip line 18 with a system associated with an antenna system to transmit signals. The signal inputted to second switch 19 is fed via a seventh strip line 20 to an input port of first receiving amplifier 4 or via an eighth strip line 22 to an input port of second receiving amplifier 9.
Lengths of the strip lines are determined such that a phase difference of 180xc2x0 appears between the transmission signal delivered via third, fourth, and first strip lines 14, 16, and 3 to first receiving amplifier 4 and that supplied via sixth and seventh strip lines 18, 20 thereto as well as between the transmission signal fed via third, fifth, and second strip lines 14, 17, and 8 to second receiving amplifier 9 and that transferred via sixth and eighth strip lines 18 and 23 thereto. Resultantly, two transmission signals having a phase difference of 180xc2x0 therebetween are inputted to an input port of each of the receiving amplifiers connected respectively to the antenna systems selected for the transmission. This resultantly attenuates power supplied to amplifiers 4 and 9 and hence prevents transmission spurious response due to signal distortion caused by amplifiers 4 and 9.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.